DURHAM, N.C. ? Duke underestimated the rape allegations against members of the lacrosse team in part because Durham police initially said the accuser “kept changing her story and was not credible,” according to a university report issued Monday.

The day after the March 13 team party where a 27-year-old black woman claimed she was raped, Durham police told campus officers that “this will blow over,” the report said. It said the woman initially told police she was raped by 20 white men, then said she was attacked by three.

Police told the Duke officers that if any charges were filed, “they would be no more than misdemeanors,” the report said.

Instead, more than a month after the party, a grand jury indicted two members of the highly ranked lacrosse team on charges of rape, kidnapping and sexual assault. District Attorney Mike Nifong has said he hoped to charge a third person.

The report was commissioned by the Duke president and prepared by Julius Chambers, a former chancellor at North Carolina Central University, where the accuser is a student, and William G. Bowen, a former president of Princeton University who is now head of the Andrew W. Mellon Foundation.

Their report does not say who at the Durham Police Department cast doubt on the accuser’s complaint. But, it said, allowing those comments to shape Duke’s thinking “was a major mistake.”